Apparatus for pulsed dispensing of liquid

ABSTRACT

An apparatus for pulsed dispensing of liquid. The apparatus includes a syringe body structure communicating with an input passage for pressurized actuation air, and communicating with an exit passage for allowing discharge of the liquid. An air input passage flow air controller is operative to increase the flow rate of the input air in accordance with a relationship that depends at least partially on a reduction of liquid volume in the syringe body structure resulting from a previous pulsed dispensing operation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of application Ser. No. 12/351,483,filed Jan. 9, 2009 (pending), the disclosure of which is incorporatedherein by reference in its entirety.

TECHNICAL FIELD

The present invention generally relates to dispensing small amounts ofliquid and, more particularly, dispensing small amounts of liquid fromsyringe-type dispensers.

Background

Various types of liquids, such as glue or adhesive, or other viscousliquids, are dispensed from a syringe using a timed pressure pulse. Thedispensing operation result in the formation of a dot of liquid on asubstrate, such as an electronic circuit board. In many applications thesize or volume of the dot dispensed during the timed pressure pulse issmall and must be held to strict tolerances.

Known syringe dispensers often utilize pressurized actuation air toforce the liquid from the syringe. That is, a short burst of pressurizedair into the syringe forces the small amount of liquid from the syringe.After successive pulsed dispensing operations, the volume of the liquidin the syringe decreases, and the remaining volume in the syringe mustfill with pressurized actuation air. As the air volume or space in thesyringe increases due to the concurrent decrease in space occupied bythe liquid volume, the time to reach the actuation air pressureincreases. Therefore, for short dispense cycle times the properactuation air pressure will not be reached, and this will affect the dotsize or liquid output volume of the successive dispense cycles. Morespecifically, if the dispensing system does not compensate for thissituation, the liquid discharge volume or dot size will decrease as thevolume of the liquid retained in the syringe decreases. One knowncompensation method is to use an actuation air pulse of varying time tocompensate for the changing air and liquid volume in the syringe. Thatis, as the liquid volume in the syringe decreases, the duration time ofthe actuation air burst is increased.

SUMMARY OF THE INVENTION

An apparatus is provided for pulsed dispensing of liquid comprising asyringe body structure and an actuation air input passage flow ratecontroller. The syringe body structure communicates with an inputpassage for pressurized actuation air and also communicates with an exitor discharge passage for the liquid to be dispensed. The air input flowrate controller is operative to increase the flow rate of the input airin accordance with a relationship that depends at least partially on areduction of liquid volume in the syringe body structure resulting fromone or more previous pulsed dispensing operations.

The air input flow rate controller may take various forms. For example,the flow rate controller may be a needle valve or a proportional valve.An air input flow rate controller can also be incorporated directly intothe syringe body structure. For example, the apparatus can include apiston mounted for reciprocating movement within the syringe bodystructure. The piston defines a liquid space on a side of the pistoncommunicating with the exit passage and an air space on a side of thepiston communicating with the air input passage. In this example, theair input flow rate controller may further comprise an elongate memberextending from the piston through the air input passage. The elongatemember reduces in diameter in a direction away from the exit passage.For example, this reduction in diameter may be in the form of acontinuous taper or, even more specifically, generally a cone-shapedelongate member.

A method of dispensing controlled amounts of liquid from a syringedispenser is also provided. The method generally comprises coupling asupply of pressurized actuation air to a syringe body structure throughan input passage. A first timed pulse of the actuation air is suppliedthrough the input passage to thereby expel a first amount of liquidthrough an exit. The input air flow rate is then increased in accordancewith a relationship depending at least partially on a reduction ofliquid volume in the syringe body structure. A second timed pulse of theactuation air is then supplied through the input passage at the higherflow rate to thereby expel a second amount of the liquid through theexit passage. This can allow, for example, the second amount to be atleast substantially the same as the first amount or, in other words, canachieve more consistent dispense volumes as the liquid volume in thesyringe dispenser decreases.

As further aspects of the method, the air input passage can have anannularly shaped cross-section and increasing the air flow rate cangenerally involve enlarging a cross sectional area of the input passage.For example, this can comprise increasing or enlarging the area of theannularly shaped cross-section. Increasing the area of the annularlyshaped cross-section can further comprise moving an elongate memberthrough the input passage, and the elongate member may be a continuouslytapered member such as a generally cone-shaped member. Supplying thefirst and second timed pulses of actuation air may further comprisesupplying the actuation air against a piston mounted for reciprocatingmovement in the syringe body structure.

Various additional details and features of the invention will becomemore readily apparent to those of ordinary skill in the art upon reviewof a more detailed description of illustrative or exemplary embodimentstaken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an apparatus constructed in accordancewith one illustrative embodiment.

FIG. 2 is a schematic view of an apparatus constructed in accordancewith an embodiment including an input passage flow rate regulatorincorporated directly into the syringe dispenser.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

FIG. 1 illustrates an apparatus 10 generally including an actuation airsupply 12 directing air through a pressure regulator 14 to a three-waysolenoid pressure selector 16. The three-way solenoid pressure selector16 provides pulses of the pressurized actuation air into a syringe 20comprised of a syringe body structure 22 and an adaptor 24. The pressureregulator 14 sets the amplitude of the air pressure pulse in a knownmanner. The pressure selector solenoid valve 16 is used to pressurizeand exhaust the air space 34 of the syringe dispenser in a known manner.Tubing 26 provides an air path between an input passage flow ratecontroller 30 and the adaptor 24.

FIG. 1 represents an apparatus that is conventional except for theprovision of the air input flow rate controller 30. The syringe bodystructure 22 includes liquid 32 to be dispensed, and occupying a certainvolume of the body structure. The syringe body structure also includesan actuation air space 34 which occupies the remaining volume. It willbe understood, therefore, that as the liquid volume 32 decreases duringsuccessive pulsed dispensing operations of, for example, dots of liquid40 through an exit or discharge passage 42, the actuation air space orvolume 34 will increase.

When the syringe is full of liquid 32, the liquid volume takes up muchof the interior volume of the syringe 20, leaving a small pressurizableair volume 34. When the air space or volume 34 is small, a small mass ofair will be required to achieve the proper actuation air pressureamplitude. However, without the air input flow rate controller 30, thedot size or discharge volume 40 of the liquid will become smaller as thevolume of the liquid 32 in the syringe 20 decreases and the air volumeor space 34 increases. That is, the air mass flowing through theactuation air input passage must increase and, therefore, air must bedirected into the air space 34 for a longer time period to pressurizethe syringe 20 to the proper actuation air pressure amplitude. The airinput flow rate controller 30, in this example, increases the crosssectional area of the input orifice or passage as the air volume orspace 34 enlarges or increases. This allows for an increased flow of airmass or mass flow rate into the syringe air space 34 and, therefore,achieves the set pressure amplitude in the same amount of time as theprevious dispense cycle. Therefore, the dispense cycle time is the sameduration even as the level of the liquid 32 in the syringe 20 decreases,thereby improving dot-to-dot volume consistency.

Controlling the air flow through the input passage of the apparatus maybe achieved in various ways using a flow rate controller. For example,the flow rate controller may be a needle valve or a proportionalsolenoid valve through which the actuation air is directed upstream ofthe air space 34. Either of these two types of valves, or other devices,may be used to vary the mass flow rate of actuation air or, in otherwords, the air mass flowing into the syringe per unit time.

FIG. 2 illustrates an illustrative embodiment in which an actuation airinput passage flow rate controller has been incorporated directly into asyringe dispenser 20′ and, more specifically, into the adaptor 24′. Inthis embodiment like reference numerals indicate like structure andfunction with respect to like reference numerals in FIG. 1, andtherefore require no further discussion. Like reference numerals withprime (′) marks refer to somewhat modified structure, as compared toFIG. 1, as will be apparent from the drawings and/or discussion herein.The syringe dispenser 20′ further includes a piston 50 mounted formovement within the syringe body structure 22 and a plunger or elongatedmember 52 extending upwardly from the piston 50, or in a direction awayfrom the exit passage 42. The plunger 52 is designed such that itscross-sectional area at the actuation air entry point or input orifice60 of the syringe body structure 22 is less than its cross-sectionalarea within the air space 34 closer to the piston 50. The plunger 52 maybe a cone-shaped member having a continuous taper. As the piston andplunger move toward the exit passage 42, the cross-sectional area of theportion of plunger 52 located at the orifice 60 decreases. Therefore,the overall annular, cross sectional orifice area through whichpressurized actuation air may enter the syringe body structure 22increases. This allows more air mass to enter the syringe body structure22 per unit time, i.e., this increases the air input flow rate. Thus,the air space 34 may be pressurized to the required amount in the sameamount of time regardless of the amount or volume of liquid 32 in thesyringe body structure 22.

As an example, the elongated member or plunger 52 used for a 30 ccsyringe can be 3.025″ in length. In this example, the orifice 60 canhave a diameter of 0.150″. The diameter of the section of the elongatedmember 52 located at the orifice 60 when the syringe is filled with aliquid is 0.1426″. The diameter of the section of the elongated member52 located at the orifice 60 when the syringe is empty of liquid is0.1031″. A viscous liquid of approximately 330 centipoise may beutilized to dispense dots of the liquid with air pressure pulses of0.100 second duration at 50 psi.

While the present invention has been illustrated by a description ofvarious preferred embodiments and while these embodiments have beendescribed in some detail, it is not the intention of the Applicants torestrict or in any way limit the scope of the appended claims to suchdetail. Additional advantages and modifications will readily appear tothose skilled in the art. The various features discussed herein may beused alone or in any combination depending on the needs and preferencesof the user. This has been a description of illustrative aspects andembodiments of the present invention, along with the preferred methodsof practicing the present invention as currently known. However, theinvention itself should only be defined by the appended claims.

What is claimed is:
 1. An apparatus for pulsed dispensing of liquid,comprising: a syringe dispenser including a syringe body structurecommunicating with an input passage having a cross sectional area forreceiving pressurized actuation air, and communicating with an exitpassage for allowing discharge of the liquid, the actuation air beingused to force an amount of the liquid through the exit passage; a pistonmounted for movement within said syringe body structure and defining aliquid space on one side of said piston communicating with the exitpassage, and an air space on another side of said piston communicatingwith the input passage; and an air input flow rate controller operativeto increase the flow rate of the actuation air through the input passagein accordance with a relationship that depends at least partially on areduction of liquid volume in the syringe body structure resulting froma previous pulsed dispensing operation, wherein said air input flow ratecontroller further comprises an elongate member extending from saidpiston through the input passage, said elongate member reducing indiameter in a direction away from the exit passage such that movement ofsaid elongate member is operative to modify the cross sectional area ofthe input passage.
 2. The apparatus of claim 1, wherein said air inputflow rate controller is operative to enlarge the cross sectional area bymoving said elongate member in a direction toward the exit passage inorder to increase the flow rate of the actuation air through the inputpassage.
 3. The apparatus of claim 1, wherein said elongate member iscontinuously tapered in a direction away from the exit passage.
 4. Theapparatus of claim 3, wherein said elongate member is a generallycone-shaped member.
 5. The apparatus of claim 3, wherein the inputpassage includes an annular orifice defining the cross sectional areabetween said elongate member and said syringe body structure, andmovement of said piston to force the discharge of liquid automaticallymoves said elongate member away from the input passage to therebyincrease the cross sectional area of said annular orifice.
 6. Theapparatus of claim 5, wherein said air space in said syringe bodystructure must be pressurized to an actuation air pressure to causemovement of said piston, and wherein the continuous taper of saidelongate member is tailored to provide sufficient flow rate of theactuation air to pressurize said air space to the actuation air pressurein a same amount of time regardless of a current position of said pistonand said elongate member within said syringe body structure.
 7. Theapparatus of claim 1, wherein said syringe dispenser further includes anadaptor coupled to said syringe body structure and including an elongatebore terminating at an outlet portion communicating with the inputpassage, and wherein said elongate member extends at least partiallythrough said elongate bore of said adaptor to selectively modify theflow rate of actuation air through said outlet portion and through theinput passage.